to the southward, can be traced in a continued line to the westward as far as the Jomard Isles, whence it turns round to the northward for ten miles further, where our examination ended.  This last may be considered as a submarine extension of the barrier, which probably reappears again above water, and passing to the northward of the Calvados Group, reaches as far as the northern entrance to Coral Haven, enclosing nearly all the high islands of the Archipelago.  The expanse of water inside when not occupied by land usually exhibits a depth of from 15 to 30 fathoms, with numerous sunken patches of coral, and several reefs which partially dry at low-water.  The shores of the islands also are generally protected by fringing coral reefs, the largest of which is that extending off the west and south side of Piron Island to a distance of seven or eight miles, with a well defined border towards Coral Haven.

At the western portion of the Louisiade Archipelago the reefs seen by us exhibit great irregularity of outline, continuity, and width.  Some are linear reefs, others atolls* more or less distinct in character, and the remainder are usually round or oval.  Viewed as a whole they form an interrupted chain, with numerous deepwater channels, which terminates in the West Barrier Reef of the chart but is connected with the coast of New Guinea by a bank of soundings, with, probably, a well-defined margin.  Many low, wooded islands are scattered along this line.  I know of no distinguishing feature presented by the coral reefs of the Louisiade compared with those which I have seen elsewhere.  One remarkable occurrence, however, connected with them, may be mentioned.  While passing in the ship the most northern point of Rossel Island, I observed upon the reef, about a hundred yards inside its outer border, a series of enormous insulated masses of dead coral rising like rocks from the shallow water.  The largest of these, examined through a good telescope from the distance of half a mile, was about twenty feet in length and twelve in height, with a well-defined high-water mark.  It formed quite a miniature island, with tufts of herbage growing in the clefts of its rugged sides, and a little colony of black-naped terns perched upon the top as if incubating.

(Footnote.  “An atoll differs from an encircling barrier reef only in the absence of land within its central expanse; and a barrier reef differs from a fringing reef in being placed at a much greater distance from the land with reference to the probable inclination of its submarine foundation, and in the presence of a deep water lagoon-like space or moat within the reef.”  The Structure and Distribution of Coral Reefs by Charles Darwin page 146.)

THEORY OF THEIR FORMATION.